U.S. patent application number 10/499358 was filed with the patent office on 2005-04-21 for filter sector for rotarydisc filters.
This patent application is currently assigned to GL & V SWEDEN AB. Invention is credited to Ek, Bo, Hagg, Conny.
Application Number | 20050082217 10/499358 |
Document ID | / |
Family ID | 20286406 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050082217 |
Kind Code |
A1 |
Hagg, Conny ; et
al. |
April 21, 2005 |
Filter sector for rotarydisc filters
Abstract
A filter sector (1) for rotary disc filters comprises two outer
walls (4, 5) of filter cloth defining a fitrate chamber (15) for
receiving filtrate that has flowed through the outer walls. The
outer walls of filter cloth are pleated to form a plurality of
ridges and valleys as seen from outside the filter sector. Two
liquid permeable support walls (11, 12) that solely support the
valleys of the two outer walls (4, 5) of filter cloth,
respectively, are arranged in the filtrate chamber and define a
filtrate channel (14) with a filtrate outlet (3).
Inventors: |
Hagg, Conny; (Huddinge,
SE) ; Ek, Bo; (Enskede, SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Assignee: |
GL & V SWEDEN AB
P. O. Box 100
Stockholm
SE
S-129 22
|
Family ID: |
20286406 |
Appl. No.: |
10/499358 |
Filed: |
June 18, 2004 |
PCT Filed: |
December 19, 2002 |
PCT NO: |
PCT/SE02/02402 |
Current U.S.
Class: |
210/331 ;
210/346; 210/486; 210/493.1 |
Current CPC
Class: |
B01D 33/23 20130101 |
Class at
Publication: |
210/331 ;
210/346; 210/486; 210/493.1 |
International
Class: |
B01D 035/12 |
Claims
1. A filter sector (1) for rotary disc filters, comprising first
and second outer walls (4,5) of filter cloth defining a filtrate
chamber (15) for receiving filtrate that has flowed through the
first and second outer walls of filter cloth, the outer walls of
filter cloth being pleated so that a plurality of ridges and
valleys are formed as seen from outside the filter sector, and
first and second liquid permeable support walls (11,21 ; 12,22)
supporting the first and second outer walls (4, 5), respectively,
the first and second support walls being arranged in the filtrate
chamber and defining a filtrate channel (14; 19) with a filtrate
outlet (3), characterized in that solely the valleys of the outer
walls (4, 5) of filter cloth are supported by the support walls
(11,21 ; 12, 22).
2. A filter sector according to claim 1, characterized in that the
support walls (11,12 ; 21,22) are at least substantially
planar.
3. A filter sector according to claim 2, characterized in that
spacers (13) join the support walls (11,12) to each other, so that
the support walls and spacers form a sector-shaped framework
(10).
4. A filter sector according to claim 3, characterized in that each
outer wall (4,5) of filter cloth is attached to a frame (6), so
that the outer wall and frame form a filter cloth unit(8; 9), and
that each filter cloth unit is releasably attached to the
sector-shaped framework (10).
5. A filter sector according to claim 2, characterized by a
sector-shaped grating (18) arranged in the filtrate chamber (15),
the support walls (11,12) abutting against the grating (18) at
mutual sides thereof.
6. A filter sector according to claim 5, characterized in that each
outer wall (4; 5) of filter cloth is attached to a frame (6) and to
the associated support wall (11; 12), so that the outer wall, frame
and support wall form a filter cloth unit (16; 17), and that each
filter cloth unit is releasably attached to the grating(18).
7. A filter sector according to claim 1, characterized in that each
support wall comprises a perforated sheet (11,12).
8. A filter sector according to claim 1, characterized in that each
support wall (21,22) is made of net (23) coarser than the filter
cloth.
9. A filter sector according to claim 8, characterized in that the
first and second support walls comprise opposite walls (21, 22) of
a net bag (23).
10. A filter sector according to claim 9, characterized by a
sector-shaped grating (24) arranged in the filtrate chamber(15),
the net bag (23) fitting on the grating (24).
11. A filter sector according to claim 1, characterized in that
each outer wall (4; 5) of filter cloth is joined to its associated
support wall (11; 12) by at least one joint element arranged on the
outer wall spaced apart from the confining edges of the filter
sector (1).
12. A filter sector according to claim 1, characterized in that
each outer wall (4; 5) of filter cloth comprises a metal net.
13. A filter cloth unit (8; 9) for use in a filter sector (1)
according to claim 6, characterized in that it comprises a frame
(6) and a pleated filter cloth (4,5) attached to the frame.
14. A filter cloth unit (16; 17) for use in a filter sector (1)
according to claim 6, characterized in that it comprises a frame
(6), a pleated filter cloth (4,5) attached to the frame, and a
liquid permeable support wall (11; 12), which supports the filter
cloth and is attached thereto.
15. A filter cloth unit (16; 17) for use in a filter sector (1)
according to claim 7, characterized in that it comprises a pleated
filter cloth (4,5) and a support wall of net (23), which is coarser
than the filter cloth and attached thereto.
16. A filter cloth unit (8; 9; 16; 17) according to claim 13,
characterized in that the pleated filter cloth comprises a metal
net.
Description
[0001] The present invention relates to a filter sector for rotary
disc filters, comprising first and second outer walls of filter
cloth defining a filtrate chamber (15) for receiving filtrate that
has flowed through the first and second outer walls of filter
cloth. The outer walls of filter cloth are pleated so that a
plurality of ridges and valleys are formed as seen from outside the
filter sector. First and second liquid permeable support walls
support the first and second outer walls, respectively, the first
and second support walls being arranged in the filtrate chamber and
defining a filtrate channel with a filtrate outlet. Filter sectors
of this kind are assembled to form circular filter discs, which are
utilized in rotary disc filters for filtering suspensions, in
particular fibre suspensions.
[0002] A known filter sector of this kind is disclosed in Swedish
Patent Application No. 9901154-6. The outer walls of filter cloth
of the known filter sector are assembled to a self-rigid filter
sector and are oriented relative to one another such that the
ridges and valleys of the filter cloths form radial channels in the
filtrate chamber. The provision of ridges and valleys gives the
known filter sector a higher filtrate capacity than traditional
filter sectors with planar walls of filter cloth.
[0003] However, it has been proved that the filter cloths of the
known filter sector according to the Swedish patent application
have a relatively poor fatigue resistance against dynamic pressure
strains acting on the filter sector during the rotation of the
filter sector through the suspension to be filtered. This results
in that the threads of the filter cloths over time are stretched
locally and finally break, so that the filtrate efficiency is
deteriorated. For this reason the filter cloths have a relatively
short lifetime and have to be exchanged for new ones too often,
which is unsatisfying.
[0004] One way of eliminating the problem of poor fatigue
[0005] One way of eliminating the problem of poor fatigue
resistance of the filter cloths is to design the outer walls from
perforated sheets, such as plates, which are profiled so that
ridges and valleys are formed, whereby the need for filter cloths
is eliminated. Such a filter sector with profiled plates is
disclosed in WO 98/11972. However, perforated and profiled plates
have many drawbacks. Perforated plates give a relatively poor
filtrate capacity, since the open area is relatively small.
Relatively expensive machining of the plates, such as punching or
drilling, is required to form the perforations. In addition, the
perforations constitute indications of fracture, which become
aggravated when profiling the plates. Such indications of fracture
can rapidly give rise to larger fractures of the plate, so that the
plate has to be replaced. For these reasons, the arrangement of
profiled and perforated plates is not any satisfactory alternative
to filter cloths.
[0006] U.S. Pat. No. 3,948,779 discloses a rotary disc filter with
filter sectors having pleated perforated support walls and filter
cloths that along their entire surfaces are supported by the
support walls. As a result, the filter cloths assume the same
pleated shape as the support walls. However, this known filter
sector is quite complicated, because it requires pleating of the
support walls to a fan-shaped form and the arrangement of rods
along the valleys of the filter cloths to secure the filter cloths
onto the support walls.
[0007] The object of the present invention is to provide a simple,
high capacity filter sector of the kind discussed above.
[0008] This object is obtained by a filter sector of the kind
initially stated characterized in that solely the valleys of the
outer walls of filter cloth are supported by the support walls. As
a result, the filter sector of the invention is much simpler than
known filter sector according to U.S. Pat. No. 3,948,779.
Furthermore, the dynamic strains that the filter sector is
subjected to during operation will substantially be carried by the
support walls, which significantly reduces the stretch of the
threads of the filter cloths, so that the lifetime of the filter
cloths is increased.
[0009] The filter cloths preferably comprises a metal net, for
example a pulp wire cloth.
[0010] Rotary filters provided with filter sectors of the kind here
presented typically have an outlet device for filtrate adapted to
receive the filtrate from the radially inner ends of the filter
sectors. Therefore, the support walls suitably form a filtrate
outlet for the filtrate channel at the radially inner end of the
filter sector. (Alternatively, however, the filtrate outlet may be
arranged at other locations on the filter sector, for example at
the radially outer end of the filter sector.)
[0011] Each support wall suitably is planar or at least
substantially planar and preferably is made of a net coarser than
the filter cloth. Alternatively, however, each support wall may
comprise a perforated sheet, for example of perforated plate.
[0012] According to a first embodiment of the invention, spacers
join the support walls to each other, so that the support walls and
spacers form a sector-shaped framework. Each outer wall of pleated
filter cloth is advantageously mounted on a frame, so that the
outer wall and the frame form a separate filter cloth unit. By
releseably attaching such a filter cloth unit to the sector-shaped
framework it will be very simple and time-saving to exchange the
filter cloth unit, in case the latter is damaged, for a new filter
cloth unit.
[0013] According to a second embodiment of the invention the filter
sector comprises a sector-shaped grating arranged in the filtrate
chamber, the support walls abutting against the grating at mutual
sides thereof. Advantageously, each outer wall of pleated filter
cloth is attached to a frame and to the associated support wall, so
that the outer wall, frame and support wall form a separate filter
cloth unit, which is releasably attached to the grating. The filter
cloth unit according to the second embodiment thus differs from the
filter cloth unit according to the first embodiment described above
in that the also the support wall is included. In the same manner
as described for the filter cloth unit according to the first
embodiment it will also be very simple and time-saving to exchange
the filter cloth unit according to the second embodiment, in case
the latter is damaged, for a new filter cloth unit.
[0014] According to a third embodiment of the invention the first
and second support walls comprise opposite walls of a net bag. In
this case the filter sector suitably comprises a sector-shaped
grating arranged in the filtrate chamber, wherein the net bag fits
on the grating. The net bag may be more or less flexible and be
made of plastic or metal.
[0015] To further counteract detrimental stretches in the threads
of the filter cloths each outer wall of filter cloth may be joined
to its associated support wall by at least one joint element
arranged on the outer wall spaced apart from the confining edges of
the filter sector, preferably centrally on the outer wall. For
example, three or more joint elements may be evenly distributed on
each outer wall. Each joint element is suitably releasable to
facilitate exchange of a damaged or worn out filter cloth. For
example, the joint element may comprise a screw joint.
Alternatively, however, it is possible to use a joint element in
the form of a permanent rivet joint, welded joint, soldered joint,
or the like. It is also conceivable to use a joint element in the
form of a glue joint, which may be permanent or releasable, for
example releasable with the aid of heat.
[0016] The invention is described in more detail in the following
with reference to the accompanying drawings, in which
[0017] FIG. 1 shows a filter sector according to the invention,
[0018] FIG. 2 shows a cross-section through a filter sector
according a first embodiment of the invention,
[0019] FIG. 3 shows the embodiment according to FIG. 2 with
disassembled parts,
[0020] FIG. 4 shows a cross-section through a filter sector
according to a second embodiment of the invention,
[0021] FIG. 5 shows the embodiment according to FIG. 4 with
disassembled parts,
[0022] FIG. 6 shows a cross-section through a filter sector
according to a third embodiment of the invention,
[0023] FIG. 7 shows a filter cloth unit of the embodiment according
to FIG. 6, and
[0024] FIG. 8 shows a sector-shaped grating of the embodiment
according to FIG. 6.
[0025] In the figures identical components have been provided with
the same reference numerals.
[0026] FIG. 1 shows a filter sector 1 according to the invention
comprising a filter cloth 2, which is pleated so that parallel
substantially radially directed ridges and valleys of the filter
cloth 2 are formed. The filter cloth 2 consists of a workable metal
net, such as pulp wire cloth. A filtrate outlet 3 for filtrate that
has flowed through the filter cloth 2 to the interior of the filter
sector 1 is arranged at the radially inner end of the filter
sector. A number of such filter sectors 1 are to be assembled to
form a circular filter disc, which is used in a rotary disc
filter.
[0027] FIGS. 2 and 3 show an embodiment of the filter sector 1,
comprising two sector-shaped outer walls 4 and 5 of pleated filter
cloth 2. The outer wall 4 and 5, respectively, is at its
circumferential edge attached to a frame 6 and 7, respectively, so
that a separate filter cloth unit 8 and 9, respectively, is formed,
see FIG. 3. At their frames 6, 7 the filter cloth units 8, 9 are
releasably attached to a sector-shaped framework 10, which
comprises two planar perforated support walls 11, 12 of plate.
Spacers 13 permanently join the support walls 11, 12 to each other,
so that they extend in parallel with each other and define a
filtrate channel 14. The filtrate channel 14 communicates with the
filtrate outlet 3. Between the two outer walls 4, 5 of filter cloth
there is formed a filtrate chamber 15 for receiving filtrate that
has flowed through the outer walls 4, 5, se FIG. 2.
[0028] During operation, filtrate flows through the outer walls 4,
5 of filter cloth and further through the perforated support walls
11, 12 into the filtrate channel 14 where the filtrate flows
further in the direction radially inwardly (towards the thinner end
of the filter sector) to the filtrate outlet 3.
[0029] FIGS. 4 and 5 show another embodiment of the filter sector
1, which differs from the embodiment according to FIGS. 2 and 3 in
a different design of the sector-shaped framework and filter cloth
units. Thus, the separate filter cloth unit 16 and 17,
respectively, also includes the perforated support wall 11 and 12,
respectively, which is attached to the outer wall 4 and 5,
respectively, see FIG. 5. At their frames 6, 7 the filter cloth
units 16, 17 are releasably attached to a frame-work in the form of
a sector-shaped grating 18, which forms a filtrate channel 19, see
FIG. 4. A number of joint elements (not shown) joining the outer
walls 4, 5 of filter cloth with their associated support walls 11,
12 may be arranged suitably centrally on the filter cloth units 16,
17.
[0030] FIG. 6 shows an embodiment of the invention that differs
from the embodiment according to FIGS. 4 and 5 in a different
design of the support walls. Thus, one single separate filter cloth
unit 20, see FIG. 7, comprises substantially planar support walls
of two opposite sides 21 and 22 of a net bag 23 and two pleated
outer walls 4, 5 of filter cloth that are attached to respective
sides 21, 22 of the net bag 23. The net bag 23 fits on a separate
sector-shaped grating 24 of a kind similar to the grating 18 of the
embodiment according to FIGS. 4 and 5.
[0031] Alternatively, like the support walls 21,22 of the
embodiment according to FIGS. 6-8 also the support walls 11,12, of
the embodiments shown in FIGS. 2-5 may be made of net.
[0032] The releasable filter cloth units 6, 7, 16, 17, 20 enable a
simple and rapid exchange of damaged or worn out filter cloths for
new ones. Thus, the single damaged outer wall of filter cloth is
not exchanged but the entire filter cloth unit is exchanged for a
new prefabricated filter cloth unit.
* * * * *